Juglans sigillata, an endemic species in China, serves as a vital local economic resource. Aluminum (Al) stress caused by soil acidification can potentially threaten the growth of J. sigillata. This study aimed to elucidate the mechanism of the alleviation of Al stress by silicon (Si) in J. sigillata. The results showed that Si could reduce the Al accumulation of walnut and improve root growth under Al stress. Si also increased peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities and soluble sugar and proline contents, reduced malonaldehyde (MDA) and H2O2 contents and the O2- production rate, and maintained the homeostasis of cells. Transcriptome analysis revealed significant up-regulation of genes encoding plant hormones (ABA, IAA, and CTK) and photosystem II components (PsbO, PsbQ, PsbW, and PsbY). Under Al stress conditions, the application of exogenous Si notably enhanced the expression of genes associated with heavy metal transport (CAX, PAA, ABC, HMA, NRAMP, and ZIP). Comprehensive transcriptome and metabolomics analysis showed that Si regulated secondary metabolite metabolism via the phenylalanine, galactose, and tryptophan pathway, altered cell wall composition, increased energy supply, and reduced auxin synthesis in root tip transition zones to alleviate Al toxicity of J. sigillata. In summary, the application of Si significantly alleviated Al-induced damage in J. sigillata.

Ascorbic acid (ASC) is a molecule naturally synthesized in plant cells, protecting against abiotic stresses by reducing reactive oxygen species (ROS), which cause oxidative damage. Aluminum (Al) toxicity is the major limiting factor on crop productivity in acidic soils, increasing ROS within cells and impairing the growth and development of plants. Exogenous antioxidant applications are an effective strategy to promote tolerance to abiotic stress. The objective was to evaluate the effect of foliar ASC applications (0, 50, 100, 200, and 400 mg L-1 ASC) and their interaction with Al toxicity (0, 400 mu M Al) in Star, an Al-sensitive cultivar of highbush blueberry. Significant increases of 1.6-fold in growth were observed in roots and leaves under treatment with 200 mg L-1 ASC. In the same treatment, increased pigments and antioxidant activity (similar to 1.2- to 2.3-fold) were observed concomitant with reduced lipid peroxidation. Positive correlations between organic acid exudation, the ASC/DHA ratio, and calcium levels were observed, whereas a negative correlation between lipid peroxidation and dehydroascorbate (DHA) was observed. Foliar ASC application also increased the ASC/DHA ratio in leaves and enhanced 2.2-fold organic acid exudation in the 200 mg L-1 ASC treatment. The results suggest that foliar ASC applications improved redox balance and underscore the potential of ASC as a practical solution to enhance resilience in Al-sensitive plants.

We identified several new TILLING mutants of barley (Hordeum vulgare L.) with missense mutations in the HvNAC8 gene, a homolog of the SUPPRESSOR OF GAMMA RESPONSE 1 (SOG1) gene in Arabidopsis thaliana. In Arabidopsis, SOG1 is the primary regulator of the DNA Damage Response (DDR) pathway. We aimed to transfer this knowledge to barley, an agriculturally important crop. Our detailed analysis of the hvnac8.k mutant revealed an impaired DDR pathway. The hvnac8.k mutant accumulates DNA damage under genotoxic stress induced by zeocin, but it also shows increased DNA damage under normal growth conditions. Despite this, the frequency of dividing cells in the root meristem of the mutant treated with zeocin is much less affected than in the wild type. This suggests that the mutant bypasses the typical DDR regulation, where cell division is halted to allow DNA repair following damage. We also analyzed our mutant under aluminum (Al3+) stress. Aluminum ions, present in acidic soils that constitute approximately 50 % of arable land, are a common stressor that significantly reduce barley yield. Al3 + is known to cause DNA damage and activate DDR. Consequently, we aimed to assess whether the hvnac8.k phenotype could confer a beneficial effect under aluminum stress, a widespread agronomic challenge. Our findings suggest that modulation of the DDR pathway has the potential to improve aluminum tolerance in barley.

AimTo examine the effect of active aluminum (Al) on copper(II) (Cu(II)) bioavailability in an acidic Cu-contaminated soil and uptake of Cu(II) by Chinese cabbage.MethodsA pot trial was conducted with Ca(OH)2 and peanut straw biochar (PB) to investigate Cu(II) uptake by Chinese cabbage. DGT (CDGT-Cu) and CaCl2 extraction methods (CCaCl2-Cu) were used to determine soil available Cu(II) and BCR sequential-extraction was used to determine Cu(II) species in the soil.ResultsThe amelioration of soil acidity with Ca(OH)2 and PB increased soil pH, promoted Chinese cabbage growth, and decreased Cu(II) uptake by plant shoots/roots. There were highly significant positive linear correlations between CDGT-Cu, CCaCl2-Cu and Cu(II) uptake by plant shoots. CDGT-Cu showed a better predictive effect for Cu(II) uptake by plant roots with a greater correlation coefficient (R2 = 0.9756). Thus, the DGT method was more effective in predicting Cu(II) uptake by plants. With increasing soil pH, Cu-HOAc and Cu-Reducible were converted to Cu-Residual, resulting in a decrease in soil Cu(II) bioavailability. The results of Structural Equation Modeling analyses showed that Al uptake by Chinese cabbage had a promoting effect on Cu(II) uptake by the plant, mainly through affecting plant growth indirectly. Soil exchangeable Al inhibited root growth (root length, root dry weight), reduced root resistance of Chinese cabbage and indirectly increased Cu(II) uptake.ConclusionsReducing Al toxicity decreased root damage and Cu(II) uptake by plant, improving the edible quality of Chinese cabbage. When remediating acidic Cu-contaminated soils, more attentions should be payed to mitigating and regulating Al toxicity.

Plants encounter various abiotic stresses throughout growth and development, with aluminum stress emerging as a major global agricultural challenge that hinders plant growth and limits crop yields in acidic soils. In this study, nanomaterials with dual functions, controlled release and adsorption, were constructed to alleviate aluminum toxicity. Specifically, two metal-organic frameworks, UiO-66 and ZIF-8, were used to load naphthylacetic acid and tryptophan, respectively. These two controlled-release systems were then combined with a chitosan-based matrix (NT@CS@UZ) to enable the regulated release of both compounds at distinct rates. Concurrently, the porous structure of these materials facilitates the adsorption of soluble aluminum in the plant rhizosphere. Results show that the acidic environment accelerates ZIF-8 degradation, triggering an early release of tryptophan under aluminum stress conditions. This early release promotes plant growth and alleviates stress damage. Naphthylacetic acid is subsequently released at a slower, sustained rate to stimulate root growth and further mitigate aluminum toxicity in roots. Additionally, NT@CS@UZ effectively adsorbs aluminum ions, limiting Al3+ uptake by plants and creating a low-aluminum barrier to protect roots. These dual function nanomaterials significantly boost crop yield and enhance stress resilience, presenting new avenues for food security and sustainable agricultural practices.

Microbial secondary metabolites are crucial in plant-microorganism interactions, regulating plant growth and stress responses. In this study, we found that cyclo(-Phe-Pro), a proline-based cyclic dipeptide secreted by many microorganisms, alleviated aluminum toxicity in wheat roots by increasing root growth, decreasing callose deposition, and decreasing Al accumulation. Cyclo(-Phe-Pro) also significantly reduced Al-induced reactive oxygen species (ROS) with H2O2, O2 center dot-, and center dot OH levels decreasing by 19.1%, 42.8%, and 17.9% in root tips, thus protecting the plasma membrane from oxidative damage. Although Al stress increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in wheat roots, cyclo (-Phe-Pro) application reduced these enzyme activities. However, compared to the Al treatment, cyclo(-Phe-Pro) application increased DPPH and FRAP activities by 16.8% and 14.9%, indicating increased non-enzymatic antioxidant capacity in wheat roots. We observed that Al caused the oxidation of ascorbate (AsA) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively. Under Al stress, cyclo (-Phe-Pro) treatment maintained reduced AsA and GSH levels, as well as high AsA/DHA and GSH/GSSG redox pair ratios in wheat roots. High AsA/DHA and GSH/GSSG ratios can reduce Al toxicity by neutralizing free radicals and restoring redox homeostasis via antioxidant properties. These results suggest that cyclo(-Phe-Pro) maintains ASA- and GSH-dependent redox homeostasis to alleviate oxidative and Al stress in wheat roots. Findings of this study establishes a theoretical foundation for using microbial metabolites to mitigate Al toxicity in acidic soils, highlighting their potential in sustainable agriculture.

Mutation breeding is a promising technique used for improving crop plants' performance, including tolerance to aluminum in rice (Oryza sativa L.) cultivars. The presented research pursued developing aluminum-tolerant rice lines through mutation in two local rice cultivars, 'Mayas' and 'Adan'. Mutation induction using six doses of gamma irradiation included 50, 100, 150, 200, 250, and 300 Gy. The evaluation of root tolerance index proceeded for early selection of aluminum tolerant lines. In addition, root swelling, aluminum absorption, cross-sectional histology, and root lipid peroxidation incurred scrutiny. The results showed gamma irradiation (100 Gy) could produce aluminum stress tolerant lines from the cultivar Mayas. Aluminum-tolerant lines obtained totaled 91 through gamma irradiation in the local rice genotypes. The morphological traits of these aluminum-tolerant mutant lines underwent accumulation only at the root tip, cross-sectional histology with sclerenchyma thickening due to organic acids, and minimal cell wall damage. These lines need further evaluation to confirm their tolerance to aluminum stress, for rice cultivation on acid soils.

Heavy metals in soil can inflict direct damage on plants growing within it, adversely affecting their growth height, root development, leaf area, and other physiological traits. To counteract the toxic impacts of heavy metals on plant growth and development, plants mitigate heavy metal stress through mechanisms such as metal chelation, vacuolar compartmentalization, regulation of transporters, and enhancement of antioxidant functions. WRKY transcription factors (TFs) play a crucial role in plant growth and development as well as in responses to both biotic and abiotic stresses; notably, heavy metal stress is classified as an abiotic stressor. An increasing number of studies have highlighted the significant role of WRKY proteins in regulating heavy metal stress across various levels. Upon the entry of heavy metal ions into plant root cells, the production of reactive oxygen species (ROS) is triggered, leading to the phosphorylation and activation of WRKY TFs through MAPK cascade signaling. Activated WRKY TFs then modulate various physiological processes by upregulating or downregulating the expression of downstream genes to confer heavy metal tolerance to plants. This review provides an overview of the research advancements regarding WRKY TFs in regulating heavy metal ion stress-including cadmium (Cd), arsenic (As), copper (Cu)-and aluminum (Al) toxicity.

Aluminum (Al), prevalent in the crust of the Earth, jeopardizes plant health in acidic soils, hindering root growth and overall development. In this study, we first analysed the Al- and pH- tolerance of the Penicillium olsonii TLL1 strain (POT1; NRRL:68252) and investigated the potential for enhancing plant resilience under Al-rich acidic soil conditions. Our research illustrates the extraordinary tolerance of POT1 to both high Al concentrations and acidic conditions, showcasing its potential to alleviate Al-induced stress in plants. Metabolite analysis revealed that POT1 detoxifies Al through organic acid-dependent chelation mechanisms, significantly reducing Al stress in Arabidopsis and Pak Choi plants. Consequently, plant growth conditions improved, and the Al content in plant tissues decreased. Transcriptome analysis indicated that POT1 treatment downregulates genes associated with Al and oxidative stress such as MATE, ALS3, NIP1-2 and several peroxidases, highlighting its effectiveness in lessening Al-induced damage. Comparative assessments highlight the superior performance of POT1 compared to other Al-tolerant Penicillium species, attributed to its ability to thrive in diverse pH levels and effectively detoxify Al. These findings position POT1 as a promising agent for enhancing crop resilience in Al-compromised acidic soils, offering new avenues for promoting plant health and bolstering food security through increased crop yield and safety.

Excessive aluminum (Al) in acidic soils is a primary factor that hinders plant growth. The objective of the present study was to investigate the effect and physiological mechanism of exogenous silicon (Si) in alleviating aluminum toxicity. Under hydroponic conditions, 4 mM Al significantly impeded the growth of white clover; however, pretreatments with 1 mM Si mitigated this inhibition, as evidenced by notable changes in growth indicators and physiological parameters. Exogenous silicon notably increased both shoot and root length of white clover and significantly decreased electrolyte leakage (EL) and malondialdehyde (MDA) content compared to aluminum treatments. This positive effect was particularly evident in the roots. Further analysis involving hematoxylin staining, scanning electron microscopy (SEM), and examination of organic acids (OAs) demonstrated that silicon relieved the accumulation of bioactive aluminum and ameliorated damage to root tissues in aluminum-stressed plants. Additionally, energy-dispersive X-ray (EDX) analysis revealed that additional silicon was primarily distributed in the root epidermal and cortical layers, effectively reducing the transport of aluminum and maintaining the balance of exchangeable cations absorption. These findings suggest that gradual silicon deposition in root tissues effectively prevents the absorption of biologically active aluminum, thereby reducing the risk of mineral nutrient deficiencies induced by aluminum stress, promoting organic acids exudation, and compartmentalizing aluminum in the outer layer of root tissues. This mechanism helps white clover alleviate the damage caused by aluminum toxicity.